Cooling of electric machines



Sept. 7 1926.

R. RDENBERG COOLING 0F ELECTRIC MAZKHINES Drgngl Filed August 2.3, 1921' Patented Sept. 7, 1926.k

UNITED STATES PATENT OFFICE.

BEINHOLD R'DENBRG, OF BERLIN-CHARLOTTENBURG, GERIVIANY, ASSIGNOR T0 SIEMENS-SCHUCKERTWERKE GESELLSCHAFT MIT B'ESCHRANKTER HAFTUNG, OF SIEMENSSTADT, NEAR BERLIN, A CORPORATION yOIE' GERMANY.

oooLnTe oF ELECTRIC MACHINES.

Original application liled August 23, 1921, Serial No. 494,546, and in Germany October 7, 1918. Divided land this application led September 16, 1924.

My invention refers to the cooling of electric machines and its particular object is to improve the out-put of suchhmachines byr improving the means for cooling them.

Such machines are constructed as a rule for a definite normal load or output and provided with a definite amount of positive (i. e. power driven) ventilation for cooling purposes, which must be of sufficient dimensions to suice for the maximum continuously required. This positive ventilation is usually embodied in the machine casing in the form of fan blades mounted in well known manner on the niachine shaft.

Arrangements are also known for automatically controlling the supply of cooling air to a. dynamo-electric machine by means of a thermostatic device affected by the teinperature of the machine so as to give a supply appropriate to the needs of the latter.

n many cases however, the maximum load or output just referred to occurs. (for example in central stations) only during a few hours of the day, and at that perhaps only during a few winter months, and therefore the machinery is underloaded or only iniperfectly utilized at all other times.

This imperfect utilization of the machinery is obviated according to the invention,

by running the machinery normally up tok a load at which it reaches the permissible limit of temperature, the case of extreme output heilig provided for by a suppleinentary or extraneous ventilation added to the ordinary normal ventilation.

This extraneous ventilation is produced by external fans or ventilatorsand conveyed into the machine.

Thus as regards the utilization of the machines, similar conditions prevail in working as exist for example in the case of steam turbines, which are fully loaded for economical utilization in the normal working, and to which fresh or live steam may be supplied for extreme outputs, thereby attaining a larger output, although with a lesser degree of eiiiciency.

Particularly favorable conditionsv in the ventilation of the machine are attained if within the load range normal or rated load and peak or excess load the air pressure Serial No. 738,082.

In order that the invention may be clear-V ly understood and readilyfcarried into effect reference will now be had by way of example to the accompanying schematic drawings in which Fig. 1 is a construction in which the sep-- :irate orvauxiliary fan works parallel with the self-ventilation fan of the machine, and

Fig. 2 a diagramcorresponding with this manner of operation.

Referring to Fig. l, m is the casing of the electric machine which is provided with a selfeventilating fan c' and a separate or auxiliary fan e is the inlet and u the outlet for the cooling air. t is the inlet for the separate fan and r the corresponding outlet. The separate fan opens into the connecting pipe s. From there the cooling air of the separate fan f enters into the casing of the electric machine at o and mixes with the current of cooling air produced by the self-venf tilating fan.

In the arrangement according to Fig. l the self-ventilator or internal fan z' and the separate or external fan f thus work in parallel to each other. In this case athe danger arises that the se'lfwcntilating fan falls off in its supply owing to the increased pressure which must be overcome when a larger quantity of cooling air is passed through the machine in case of overloads.

According to my invention this can be avoided by so diinensioniiig the self-ventilator that it supplies approximately the same quantity of air at the air pressure which corresponds with the rated load as well as at overloads.

The characteristic between the air pressure and the quantity of air of the ventilator will Within this range be substantially vertical as shown in the diagram Fig. 2.

The curve G in Fig. 2 shows in dependence from the quantity of cooling air Q iiowing through the machine theair pressure P to be expended therefore which increases approximately as the square ot the quantity ot' air. The curve V shows the characteristic of the self-ventilator, that is to say the relationship ot' its air pressure to the quantity of cooling air it will deliver. The point of intersection a 1oetiveen the ventilator characteristic and the resistance curve corresponds to the normal working point. Suppose that in the case of an extreme output, the point o the curve G corresponds to the adequate cooling of the machine, A pressure Pb must be applied, in order to torce throngl the generator the necessary quantity of air Q1, against the resistance in the air ducts of the generator7 this quantity QD being made up ot' the quantity Q@ dne to the primary ventilator and the quantity Qi due to the auxiliary ventilator, both veiitilators novvv Working under the same pressure.

it now the ventilator characteristic V drops steeply or vertically within the range of pressure nec Msary for the passage ot the cooling air through the machine, the ordi nary ventilator Still delivers approximately the Same or its maximum volume oi air under the altered conditions and is thas fully or economically' utilized, Whilst the auxiliary ventilator supplies the extra volume Qi.

For the separate ventilation according to the invention it is essential thatthe self Ventilator is from the beginning so dimensioned that it can supply the higher presenre without an excessive drop in the quantty of the air when it operates in parallel with the separate tan.

l am aware that arrangements for controlling the temperature of dynamo electric inaehinery either automatically or thermostat ically have been proposed before, and I do not claim such per se.

What l claim as my invention and desire to secure by Letters Patent is In electric machines in combination, selfventilating means diniensioned tor the normal load of said machine only and separate vcntilating means` adapted to operate parallel with said self-Ventilating means to supply ventilation t'or excess machine loads, said self-ventilating meansl being adapted to furnieh constantly approximately the .same air volume within the limits of normal and excen-s load, the ventilating currents of both ventilating means passing in common thru the machine.

ln testiniony whereof l aflix my signature.

RELYHOLD RDENBERG. 

